Mitt Romney's campaign is amending the financial disclosure form he filed in 2011 to acknowledge that a Romney trust earned interest income from a Swiss bank account, a detail that had been missing from the report.

"An amendment is being filed to address this minor discrepancy," a campaign official told ABC News in an email Thursday in response to questions about the apparent omission.

"The inescapable fact is that by releasing over 600 pages of information regarding his finances, Mitt Romney is clearly coming down on the side of disclosure," said Andrea Saul, a campaign spokeswoman, in a subsequent statement. "Any document with this level of complexity and detail is bound to have a few trivial inadvertent issues. We are in the process of putting together some minor technical amendments, which will not alter the overall picture of Gov. and Mrs. Romney's finances as disclosed in August."

The discovery that the Romneys had $3 million in an account with the Swiss bank UBS came only after the Republican presidential candidate released his tax returns for 2010 on Tuesday. The campaign had maintained that it was not necessary to disclose the Swiss account because Romney's money manager, Brad Malt, had shuttered it in early 2010.

Several Republican election lawyers told ABC News Thursday that the account still needed to be disclosed because a Romney trust earned about $1,700 in income on the account during 2010. The campaign's decision to amend the forms was first reported by the Los Angeles Times.

At the same time, questions from ABC News about undisclosed income that appeared on Newt Gingrich's tax return have led Gingrich to announce that he, too, will be amending his financial disclosure report. Gingrich's returns showed he received $252,500 in wages from Gingrich Holdings Inc. in 2010, but those wages do not appear anywhere on his presidential disclosure report.

"An internal account review found the need to amend the reporting," said a Gingrich campaign official. "It was done immediately."

Romney also decided to amend the report from his 2007 run for president, a decision first reported by the New York Times. That form identified a UBS money market account, but did not clarify that it was held by his wife's trust. UBS has branches in the United States, so it would not have been readily apparent that the account was in Switzerland. Those who track the finances of presidential candidates said they found the failures to disclose these key financial details distressing. Bill Allison, editorial director of the non-profit watchdog group the Sunlight Foundation, said the whole purpose of the disclosure reports is for candidates to provide an honest look at their finances to voters.

"Obviously, if you don't give them the information before the vote, it defeats the whole purpose of disclosure," Allison said.

Melanie Sloan, executive director of the non-partisan group Citizens for Responsibility and Ethics in Washington said she, too, was dismayed -- noting that while in Congress, Gingrich had been called out for failing to include information on his disclosure reports.

"You'd think someone once sanctioned by the House of Representatives ... would be a little more careful with his financial disclosure forms," she said.

The discovery that Romney's vast holdings included an account in Switzerland, a country long notorious for helping the very wealthy hide their assets, came during his release of his tax return earlier this week. Malt, who oversees Romney's blind trusts, acknowledged during a conference call with reporters that he decided to shut down the Swiss account because he worried it could create a headache for Romney's campaign. "It might or might not be consistent with Governor Romney's political views," he said. "The taxes were all fully paid … it just wasn't worth it. And I closed the account."

That suggests, Allison said, that the campaign had a motivation to exclude any evidence of the Swiss account from the candidate's forms. The Romney campaign called the omission an oversight.

Allison noted that there is generally no penalty for a candidate who leaves something off a disclosure report, and then goes back to amend the report if the missing information is discovered.

"Nobody is going to get into trouble for this," he said. "That is the problem with the disclosure system."